Various processes and catalysts exist for the homopolymerization or copolymerization of olefins. For many applications, it is desirable for a polyolefin to have a high weight average molecular weight while having a relatively narrow molecular weight distribution. A high weight average molecular weight, when accompanied by a narrow molecular weight distribution, provides a polyolefin with, among other things, high strength properties.
Traditional Ziegler-Natta catalysts systems—a transition metal compound co-catalyzed by an aluminum alkyl—are typically capable of producing polyolefins having a high molecular weight, but with a broad molecular weight distribution.
More recently a catalyst system has been developed wherein the transition metal compound has two or more cyclopentadienyl ring ligands—such transition metal compound being referred to herein as a “metallocene—which catalyzes the production of olefin monomers to polyolefins. Accordingly, titanocenes, zirconocenes and hafnocenes, have been utilized as the transition metal component in such “metallocene” containing catalyst system for the production of polyolefins and ethylene-alpha-olefin copolymers.
Organometallics 1998, 17, 4897 discloses exo,exo-bis(isodicyclopentadienyl)titanium and zirconium dichloride derivatives with PR2 substitutions on the Cp ring. The paper includes use of the compounds as olefin polymerization catalysts.
WO 98/07760 discloses bis(1-diphenylphosphanylindenyl)zirconium dicloride.